Ultrasonic diagnostic equipments are widely used for the medical examination. However, it is difficult for the doctor to obtain a comprehensible image while pressing the ultrasonic probe. An ultrasonographic image is taken by pressing the probe. And the image recognition is related to a contrast. Therefore, a contact force relates the image contrast. As a prototype, we developed an ultrasonic probe positioning robot. Consequently, this robot is made to measure the relation between the contact force and the image contrast. The experiment investigated the relation between the contact force and the image contrast, and controlled contact force by the image contrast. The result shows that the image contrast controls the contact force and if an error of contrast exists, the contact force is controlled the constant value at the point of the saturated image contrast.
